Alterations in left atrial (LA) and left ventricular (LV) compliance and arterial and coronary sinus atrial natriuretic factor (ANF) concentrations at baseline and in response to both volume depletion and expansion were investigated in 15 conscious dogs with aortic banding induced LV hypertrophy (H) (LV/body weight ratio increased by 64 %), which also induced LA H (LA/body weight ratio increased by 61%). With volume expansion coronary sinus ANF increased more, p<0.05, in dogs with LVH (+427q88 pg/ml), compared with control dogs (+146q45 pg/ml). Arterial ANF levels also rose more with volume expansion in LVH. In dogs with LVH, the LV end-diastolic pressure-diameter relationship was shifted to the left with a steeper slope with volume expansion, such that at any given diastolic dimension, diastolic pressure was higher. In contrast, the pressure-dimension relationship for the LA appendage was shifted in the opposite direction during both atrial systolic and diastolic phases with a more shallow slope in hypertrophy compared to control dogs, resulting in an augmented pressure-dimension product during volume loading in LAH. In conclusion, in dogs with LVH and LAH, enhanced ANF was revealed in the coronary sinus and systemic circulation during volume expansion, which could be due, in part, to a more compliant,